users: refactor password reset flow.

The old password reset flow:

* User requests a password reset.
* Danbooru generates a password reset nonce.
* Danbooru emails user a password reset confirmation link.
* User follows link to password reset confirmation page.
* The link contains a nonce authenticating the user.
* User confirms password reset.
* Danbooru resets user's password to a random string.
* Danbooru emails user their new password in plaintext.

The new password reset flow:

* User requests a password reset.
* Danbooru emails user a password reset link.
* User follows link to password edit page.
* The link contains a signed_user_id param authenticating the user.
* User changes their own password.

app/mailers/application_mailer.rb

@@ -0,0 +1,3 @@
+class ApplicationMailer < ActionMailer::Base
+  default from: "#{Danbooru.config.canonical_app_name} <#{Danbooru.config.contact_email}>", content_type: "text/html"
+end

app/mailers/maintenance/user/password_reset_mailer.rb

@@ -1,17 +0,0 @@
-module Maintenance
-  module User
-    class PasswordResetMailer < ActionMailer::Base
-      def reset_request(user, nonce)
-        @user = user
-        @nonce = nonce
-        mail(:to => @user.email, :subject => "#{Danbooru.config.app_name} password reset request", :from => Danbooru.config.contact_email)
-      end
-
-      def confirmation(user, new_password)
-        @user = user
-        @new_password = new_password
-        mail(:to => @user.email, :subject => "#{Danbooru.config.app_name} password reset confirmation", :from => Danbooru.config.contact_email)
-      end
-    end
-  end
-end

app/mailers/user_mailer.rb

@@ -1,10 +1,14 @@
-class UserMailer < ActionMailer::Base
+class UserMailer < ApplicationMailer
   add_template_helper ApplicationHelper
   add_template_helper UsersHelper
-  default :from => Danbooru.config.contact_email, :content_type => "text/html"
 
   def dmail_notice(dmail)
     @dmail = dmail
     mail(:to => "#{dmail.to.name} <#{dmail.to.email}>", :subject => "#{Danbooru.config.app_name} - Message received from #{dmail.from.name}")
   end
+
+  def password_reset(user)
+    @user = user
+    mail to: "#{@user.name} <#{@user.email}>", subject: "#{Danbooru.config.app_name} password reset request"
+  end
 end